The present invention is directed to a process for recovery of polyester film by stripping coated polyester film wherein the stripped film is of sufficient quality to recycle as a feedstock such as for direct extrusion.
Polyester film is conventionally used as a self-supporting substrate for coatings in diverse applications including photographic films, flexible packaging, and magnetic media. Photographic films utilize an adhesive coating layer to provide adhesion of a light-sensitive emulsion layer, typically a silver halide dispersed in gelatin, to the polyester film since the gelatin does not adhere well to the uncoated polyester surface. Typical adhesive coating layers used in photographic films include polyvinylidene chloride or acrylic copolymers containing acrylonitrile or vinylidene chloride.
It is desirable to strip the coating layers from discarded coated polyester films to minimize solid waste disposal and recover polyester and, in the case of x-ray and photographic films, silver constituents for recycling. Various methods have been employed to recover the silver and the polyester film from both unused ("green") and used ("black") photographic film as well as polyester film from non-silver-containing coated film. The photographic emulsion layer can be readily stripped from the underlying adhesive coating layer on the polyester film simply by subjecting the film to hot water and then the adhesive coating layer can subsequently be removed, for example, by dissolution in appropriate glycol solvents or by stripping in an aqueous alkaline stripping solution. Alternatively, the emulsion and adhesive coating layers can be stripped simultaneously, for example, by mixing the chopped photographic film flake in a hot aqueous alkaline stripping solution under high shear as described in U.S. Pat. No. 4,799,954 by Hochberg.
The prior art teaches incorporation of specific salts and surfactants in aqueous alkaline stripping solutions to disperse solid residue resulting from coating layers stripped from the polyester film. Personnette in U.S. Pat. No. 5,055,139 issued Oct. 8, 1991, teaches the use of a combination of at least 0.75 wt% trisodium phosphate and at least 0.75 wt% of alkali metal hydroxide to strip polymeric coatings from polyester substrates with recycle of the stripping solution after filtration to remove suspended coating solids. Schwartz in U.S. Pat. No. 5,286,463 issued Feb. 15, 1994, teaches a process for stripping photographic films with aqueous alkaline stripping compositions which include wetting agents, rinse aids, emulsifiers and a reducing sugar to prevent deposition of particles formed from the adhesive coating layer on the cleaned polyester film.